Energy Targets for Buildings

Derbys Eco-Centre 600With the UK Government’s decision to scrap Zero Carbon energy targets for new buildings comes the opportunity to consider better and more practical targets to minimise energy use in the near (25 years) future.

The problem with the Zero Carbon energy target was that it addressed only one form of building energy use (Operational) whilst ignoring Embodied energy – the energy used to manufacture the materials for the buildings that would use the operational energy. If this was relatively small, this really wouldn’t be a problem, but for a modern building constructed of conventional building materials (steel, concrete, masonry, timber), this can be the equivalent to 30 years or more of operational carbon – carbon emitted before the building is even occupied. And this is only the “Initial” embodied carbon – the carbon used to first construct the building; to this must be added the “Recurring” embodied carbon – the carbon required to maintain and refurbish the building over its lifecycle and maintain its’ fitness for purpose and use.

This “recurring” carbon can be relatively minor but frequent – cleaning, for example, or more significant but less frequent – replacement of carpets & finishes or redecoration. However, at some point of the building’s life, a major refurbishment may be take place, for example replacement of the building’s roof or walls – a significant future expenditure of carbon. Or repurposing to make the building suitable for a different use.

Is there a better alternative? Yes, there is – to give all new buildings a “Carbon Budget” for the next 25 years based on total energy use: Initial Embodied (IE) + Operational (O) + Recurring Embodied (RE). For commercial buildings, this could be “functional” for example “Per square metre of internal floor area”, whilst for domestic this could be performance based “Per occupant” (based on say design bedroom occupancy). However it’s measured, the impact would be the same. It wouldn’t matter whether the design was simple (low IE) but with higher operational (O) emissions, or complex (high IE / RE) with low “O” – after 25 years, the total carbon emissions would be exactly the same.

And if you want to improve the performance of buildings year by year, simply reduce their Carbon Budget.

(I’ve written about this topic before – you can read my 2011 article on this here)

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